A  Revision  of  the  Atomic  Weight  of  Antimony 
The  Analysis  of  Antimony  Bromide 


A  DISSERTATION 


SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY  IN  THE  UNIVERSITY 
OF  MICHIGAN. 


BY 


ROY  KENNETH  McALPINE 
1920 


EASTON,  PA.: 

ESCHENBACH  PRINTING  Co. 
1921 


A  Revision  of  the  Atomic  Weight  of  Antimony 
The  Analysis  of  Antimony  Bromide 


A  DISSERTATION 


SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS  FOR 
THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY  IN  THE  UNIVERSITY 
OF  MICHIGAN. 


BY 

ROY  KENNETH  McALPINE 

c 

1920 


EASTON,  PA.: 

ESCHENBACH  PRINTING  Co. 
1921 


ACKNOWLEDGMENT. 

For  the  valuable  guidance  and  constant  interest  of  Professor  H.  H. 
Willard,  under  whose  supervision  this  investigation  was  carried  out,  and 
for  the  kindly  interest  and  encouragement  of  Professor  M.  Gom$etg,\{ 
wish  to  express  my  most  grateful  appreciation. 

ROY  KENNETH 
ANN  ARBOR,  MICH., 
October,  1920. 


CONTENTS. 

Page. 

Introduction 5 

Historical  Review 6 

Preparation  of  Materials 10 

Pure  Bromine 10 

Pure  Silver 10 

Accessory  Reagents 10 

Pure  Antimony 11 

.    .  Purification  of  Antimony  Compounds 11 

'   I  '.,» '.  '    !  Recovery  of  the  Metal 13 

.  Antirnpny  Bromide .  14 

'.  '•  . .  I  Construction  of  Apparatus 14 

Preparation  of  Samples 17 

Analysis  of  Antimony  Bromide 19 

Balance  and  Weighing.  .  19 

Methods  of  Analysis 21 

Preliminary  Studies 

Final  Analyses 26 

Note  on  Cooke's  Bromide 27 

Summary  and  Conclusion 


A  REVISION  OF  THE  ATOMIC  WEIGHT  OF  ANTIMONY. 
THE  ANALYSIS  OF  ANTIMONY  BROMIDE. 

Introduction. 

It  requires  only  a  cursory  glance  at  the  earlier  reports  of  the  Inter- 
national Committee  on  Atomic  Weights  to  learn  that  the  value  in  the 
tables  to-day  for  the  atomic  weight  of  antimony  rests  on  no  secure  basis. 
It  was  put  forth  in  19031  as  a  compromise  between  Cooke's  work  on  the 
bromide,2  pointing  to  120.0,  and  the  work  of  Cooke3  and  of  Schneider4 
on  the  sulfide  and  the  work  of  Friend  and  Smith5  on  tartar  emetic,  the 
three  latter  giving  values  ranging  from  120.22  to  120.55. 

Careful  examination  of  the  papers  dealing  directly  with  the  analytical 
problem  shows  that  the  uncertainty  is  much  greater  actually  than  the 
above  would  indicate.  Disregarding  the  work  of  Berzelius,6  from  which 
he  selected  the  number  129,  as  well  as  the  earlier  work  of  Kessler,7  which 
he  himself  later  corrected  for  known  errors,  the  other  determinations 
group  themselves  into  two  main  divisions  approximating  120  and  122. 
Thus  Dexter8  (1857),  Dumas9  (1859),  and  Kessler10  (1860),  obtained 
122.46,  121.83  and  122.08-122.33,  respectively,  on  the  basis  of  which 
the  number  122  was  generally  adopted.  Schneider11  (1856),  however, 
had  analyzed  a  native  sulfide  of  antimony,  the  data  pointing  to  the  num- 
ber 120.55,  and  Cooke12  (1877-81)  made  a  laborious  study  including 
syntheses  of  antimony  trisulfide  and  the  estimation  of  halogen  in  the  tri- 
halides  of  antimony,  which  was  so  convincing  that  it  immediately  estab- 
lished the  lower  value,  120. 

Cooke's  last  data  on  the  ratios,  SbBr3  :  3Ag  and  SbBr3  :  3AgBr,  pre- 
sented a  concordance  of  results  unknown  to  chemical  analysis  of  that  day, 
and  are  credited  by  Brauner13  with  introducing  the  modern  era  of  atomic 
weight  determinations. 

1  /.  Am.  Chem.  Soc.,  25,  2  (1903);  Z.  physik.  Chem.,  42,  634  (1903);  Proc.   Chem. 
Soc.,  19,  2  (1903);  Ber.,  36,  5  (1903). 

2  Proc.  Am.  Acad.  Arts.  Sci.,  15,  251  (1880);  ibid.,  17,  1  (1881). 

3  Cooke,  Proc.  Am.  Acad.  Arts  Sci.,  13,  1-37  (1877). 

4  Schneider,  Pogg.  ^ww.,97,483;  and  98,  293  (1856);  J.  prakt.  Chem.,  22, 131  (1880). 

5  Friend  and  Smith,  J.  Am.  Chem.  Soc.,  23,  502  (1901). 

6  Berzelius,  Pogg.  Ann.,  8,  1  (1826). 

7  Kessler,  ibid.,  95,  204  (1856). 

8  Dexter,  ibid.,  100,  563  (1857). 

9  Dumas,  Ann.  chim.  phys.,  [3]  55,  175  (1859). 

10  Kessler,  Pogg.  Ann.,  113,  134  (1860). 

11  Schneider,  ibid.,  97,  98,  293,  483  (1856). 

12  Cooke,  Proc.  Am.  Acad.  Arts  Sci.,  13,  1  (1877);  ibid.,  17,  1  (1881). 

13  Brauner,  Abegg's  "Handbuch  d.  anorg.  Chem."  [Ill]  3,  558  (1907). 


458725 


G 

The  electrochemical  studies  of  Pfeiffer1  (1881)  and  of  Popper2  (1886) — 
generally  regarded  as  discredited  by  the  work  of  Cohen,  Collins  and 
Strengers3— gave  122.36-121.36  and  121.20,  respectively.  Bongartz4 
(1883),  from  a  complex  process,  derived  the  value  120.64  from  the  ratio, 
2Sb  :  3BaSC>4,  and — last  in  the  field  of  ostensible  atomic  weight  studies — 
Friend  and  Smith5  obtained  the  value  120.43  from  the  ratio  KSbOC4H4O7: 
KC1. 

From  the  time  of  Becker's  "Digest  of  Atomic  Weight  Determinations" 
(1880)  down  to  Brauner's  article  in  Abegg's  "Handbuch"  (1907),  Cooke's 
work  on  the  bromide  of  antimony  so  prejudiced  the  reviewer  that  the  dis- 
cussion of  the  original  papers  was  decidedly  uncritical  and  at  times  in- 
accurate as  to  facts.  Compare,  as  a  case  in  point,  the  easy  dismissal  of 
the  work  on  antimony  chloride  (Dumas,  121.83;  Cooke,  121.84)  on  the 
basis  of  Cooke's  first  suggestion  of  some  oxy chloride  in  the  material 
studied,6  with  the  fact  that  Cooke  offered  two  different  explanations  for 
these  high  numbers,7  neither  of  which  was  adequately  supported  by 
his  own  experimental  data.8 

Note,  further,  such  comments  as  that  of  Richards9  that  "much  of  the 
voluminous  work  on  the  subject  is  now  rejected  by  common  consent," 
and  that  of  Clarke,10  "the  higher  values,  say  all  over  121,  are  almost  cer- 
tainly in  error  and  ought  to  be  rejected." 

Anticipating  the  results  obtained  in  the  present  study  it  may  not  be 
out  of  place  to  insert  a  brief  critical  review  of  the  past  work  bearing  on 
the  atomic  weight  of  antimony  from  the  point  of  view  of  indicating  proba- 
ble major  errors. 

Historical  Review. 

A  table  adapted  chiefly  from  Clarke's  Recalculations,  3rd  edition,  and 
Brauner's  Summary  in  Abegg's  "Handbuch  der  anorganischen  Chemie.'' 

Name.  Year.  Ratio  det.  Atomic  wt.  Sb. 

1.  Berzelius     ,  1812  2Sb  :  Sb2O4  129.0 

2Sb:Sb2S3  128.9 

2.  Kessler  (1st  paper)  1855  volumetric  studies  123.6-123.8 

3.  Schneider  (1st  paper)  1856  Sb2S3  :  2Sb  120.55 

4.  Dexter 1857  2Sb  :  Sb2O4  122 .46 

5.  Dumas  1859  SbCl3  :  3AgCl  121.83 

1  Pfeiffer,  Ann.,  209,  174  (1881). 

2  Popper,  ibid.,  223,  153  (1886). 

8  Cohen,  Collins  and  Strengers,  Z.  physik.  Chem.,  50,  308  (1904). 

4  Bongartz,  Ber.,  16,  1942  (1883). 

6  Friend  and  Smith,  J.  Am.  Chem.  Soc.,  23,  502  (1901). 

6  See  Brauner,  loc.  cit.     Clarke,  Recalculations  of  the  Atomic  Weights. 

7  Proc.  Am.  Acad.  Arts  Sci.,  13,  70  (1877);  ibid:,  17,  22  (1881). 

8  Loc.  cit. 

3  Richards,  Am.  Chem.  J.,  20,  546  (1898). 

10  Clarke,  Recalculation  of  the  Atomic  Weights,  3rd  edition,  p.  327. 


6.  Kessler  (2nd  paper)  1861  Sb2Oa  :  2O  122.08 

Sb  :O  122.33 

7.  Cooke  (1st  paper)  1877          2Sb  :  Sb2S3  120.22 

SbCl3:3AgCl  121.84 

SbCl3  :  Sb  121.91 

SbBr3  :3AgBr  119.88 

SbI3:3AgI  119.86 

8.  Cooke  (later  papers)  1880  SbBr3  :  3AgBr  119.88 

1881  SbBr3:3Ag  119.97 

9.  Schneider  (2nd  paper)  1880  Sb2S3  :  2Sb  120.41 

10.  Pfeiffer  1881  3Cu  :  2Sb  122.36 

3Ag  :  Sb  121 .36 

11.  Bongartz  1883  2Sb  :  3BaSO4  120.64 

12.  Popper  1886  3Ag  :  Sb  121.20 

13.  Friend  and  Smith  1901  KSbOC4H4O7  :  KC1         120.43 

14.  Beckett  1909  Sb2S3  :  2Sb  121.54 

Sb,.S3  :  3BaSO4  121 .66 

Sb2S3:4I  122.08 

(Although  not  ostensibly  dealing  with  the  atomic  weight  of  antimony,  the  quanti- 
tative studies  on  antimony  by  E.  G.  Beckett  (1909)  have  distinct  bearing  on  the  ques- 
tion and  are  worthy  of  inclusion  in  this  table.) 

The  references  to  the  original  papers  are  as  follows:  1.  Pogg.  Ann.,  8,  1  (1826. 
2.  Pogg.  Ann.,  95,  204  (1855).  3-  Pogg.  Ann.,  97,  483;  Ibid.,  98,  293  (1856).  4, 
Pogg.  Ann.,  100,  563  (1857).  5.  Ann.  chim,  phys.,  (3)  55,  175  (1859J.  6.  Pogg.  Ann., 
113,  134  (1860).  7.  Proc.  Am  Acad  Arts  Sci.,  13,  1-71  (1877).  8.  Proc.  Am.  Acad. 
Arts  Sci.,  15,  251  (1880);  Ibid.,  17,  1-22  (1881).  9.  J.  prakt  Chem.,  (2)  22,  131  (1880). 
10.  Ann.,  209,  174  (1881).  11.  Ber.,  16,  1942  (1883).  12.  Ann.,  223,  153  (1886). 
13.  J.  Am.  Chem.  Soc.,  23,  502  (1901).  14.  Inaug.  Dissertation,  Zurich,  1909. 

The  following  partial  list  of  suggestions  may  help  in  the  interpreta- 
tion of  the  above  papers. 

1.  Berzelius.     The  number   129,   from  converting  a  given  weight  of 
metal  to  the  oxide,  indicates  that  too  high  a  temperature,  or  partial  re- 
duction by  gases  from  the  flame,  may  have  caused  appreciable  volatiliza- 
tion of  Sb2O3.     The  number  128.9  from  converting  metal  to  sulfide  may 
be  obtained  from  partial  oxidation  of  the  sulfide  through  exposure  to  air 
during  the  drying  process. 

2.  Kessler 's  earlier  paper  is  corrected  in  the  second  one. 

3.  Schneider's  first  paper  is  essentially  identical  with  the  second  one. 

4.  Dexter.     The  number  122.40  may  be  somewhat  too  high  from  too 
high  a  temperature  of  ignition  of  the  Sb2O4,  or  from  slight  reduction  to 
the  more  volatile  Sb2O3  in  the  closed  crucible  by  flame  gases. 

5.  Dumas.     The  number  121 .83  may  be  within  the  experimental  error 
of  the  silver  chloride  method  as  used. 

6.  Kessler's  second  paper.     The  volumetric  studies  giving  values  rang- 
ing from  122. OS  to  122.33  may  be  somewhat  high,  due  to  failure  to  guard 
sufficiently  against  oxygen  of  the  air  as  an  accessory  oxidizing  agent  the 
presence  of  which  might  lower  slightly  the  amount  of  standard  oxidizing 
agent  required. 


8 

7.  Cooke's  first  paper.     The  sulfide  studies  may  have  pointed  to  too 
low  a  value  from  impurity  in  the  antimony  sulfide  giving  too  high  a  weight. 
Aside  from  carbonaceous  residue  from  the  tartaric  acid — which    may  in 
part  have  been  counterbalanced  by  slight  solubility  of  antimony  sulfide 
and  by  slight  loss  by  sublimation  during  drying — it  has  been  shown  by 
Beckett,1  by  Hallmann,1  and  others,  that  dried  antimony  sulfide  usually 
contains  several  tenths  of  a  per  cent,  of  chlorine.     Simple  calculations 
shows  that  0.183%  chlorine  replacing  sulfur  in  antimony  sulfide  would 
cause  an  increase  of  0.1%  in  the  weight  of  the  precipitate. 

In  the  antimony  chloride  studies  chlorine  was  determined  as  silver 
chloride  and  antimony  as  antimony  sulfide  (using  the  empirical  factor 
derived  from  earlier  work  on  sulfide  for  the  calculation).  The  results, 
121.84  and  121.91,  may  indicate  some  slight  error  in  the  composition 
of  the  material  studied  but  are  within  the  permissible  error  for  ordinary 
quantitative  analysis  if  compared  with  the  value  established  in  this  pres- 
ent paper. 

The  work  on  the  bromide  and  on  the  iodide  of  antimony,  giving  119.88 
and  119.86,  respectively,  is  probably  vitiated  by  inaccuracy  in  the  com- 
position of  materials  to  which  the  formulas  SbBr3  and  SbI3  were  assigned. 
Such  inaccuracy  may  be  related  to  the  known  readiness  with  which  bro- 
mides and  iodides  take  up  hydrobromic  and  hydroiodic  acid  with  forma- 
tion of  complex  compounds. 

8.  Cooke's  second  paper.     The  values  119.88  and  119.97  derived  from 
further  study  of  antimony  bromide  are  probably  subject  to  errors  of  the 
type  suggested  with  respect  to  the  earlier  work  on  iodide  and  bromide  of 
antimony. 

9.  Schenider  (second  paper).     The  value  120.41  rests  on  the  assump- 
tion that,  aside  from  0 . 189%  determined  impurities,  the  material  studied 
consisted  of  pure  Sb2S3.     The  circumstance  noted  by  Schneider,   that, 
"on  heating  in  hydrogen  the  material  decrepitated  with  a  slight  burned 
odor  arising,"2  makes  it  seem  very  probable  that  there  was  a  certain 
amount  of  organic  material  in  this  native  stibnite  and  that  the  loss  in 
weight  on  reducing  the  sulfide  in  hydrogen  was  too  high  by  the  amount 
that  such  material  would  lose  during  such  a  process.     This  would  make 
the  apparent  atomic  weight  of  antimony  too  low. 

10.  Pfeiffer.     The   electro-chemical   comparisons   of   copper  and   anti- 
mony (at.  wt.  Sb  =  122.36)  are  subject  to  the  inaccuracies  of  the  copper 
coulometer.     The  comparison  of  silver  and  antimony  (Sb  =  121.36)  in 
the  light  of  the  later  experimental  data  of  Cohen,  Collins  and  Strengers 

1  Loc.  cit. 

2  Loc.  cit.,  p.  137. 


9 

suggests  the  possibility  of  insufficient  guarding  against  slight  evolution 
of  hydrogen  or  slight  absorption  of  oxygen  in  the  antimony  cell,  either  of 
which  effects  would  make  the  calculated  atomic  weight  of  antimony  too 
low. 

11.  Bongartz.     Even    granting    that    the    reaction    Sb2S5  +  6HC1  = 
2SbCl3  +  3H2S  +  S  is  sufficiently  exact  to  form  a  step  in  atomic  weight 
work,  details  are  lacking  that  would  be  required  to  pass  judgment  on 
such  points  as  the  possible  amount  of  occlusion  of  BaCl2  by  the  BaSO4. 

12.  Popper.     Essentially  the  same  as  Pfeiffer's  later  work  and  subject 
to  the  same  errors. 

13.  Friend  and  Smith.     The  assumption  that  tartar  emetic,  dried  at 
150°  for  16  hours,  undergoes  no  trace  of  oxidation  or  partial  decomposi- 
tion is  not  sufficiently  assured  by  the  data  presented.     Certainly,   150° 
is  getting  rather  close  to  the  temperature  at  which  further  decomposi- 
tion with  loss  of  1/2  molecule  of  water  has  been  observed. 

14.  The  work  of  Beckett,  a  study  of  quantitative  methods  for  the  de- 
termination of  antimony,  is  in  distinct  accord  with  the  present  study. 

The  controversy  as  to  the  atomic  weight  of  antimony  was  not  settled 
by  the  adoption  of  the  present  value  in  the  tables.  It  is  true  that  Henz,1 
Vortmann  and  Metzl,2  Kolb  and  Formhals,3  Hallmann4  and  others, 
studying  quantitative  methods  for  antimony,  found  the  present  value 
satisfactory;  but  Youtz,5  Beckett,6  and  Von  Bacho,7  presented  data 
pointing  to  a  distinctly  higher  atomic  weight,  and  Treadwell8  expressed 
the  belief  that  the  older  number,  122,  was  nearer  the  truth  than  the  new 
•one. 

This  last  opinion  was  undoubtedly  based  on  the  analytical  work  of 
Beckett,  done  in  Treadwell's  laboratory.  In  chief  part,  Beckett  prepared 
.a  very  pure  sample  of  antimony  trisulfide  and  obtained  data  for  the  ratios 
:Sb2S3  :  2Sb,  Sb2S3  :  3BaSO4,  and  Sb2S3  :  41,  corresponding  to  the  atomic 
weight  values  121.54,  121.66  and  122.08,  respectively.  This  work, 
while  carried  on  with  few  of  the  refinements  of  atomic  weight  practice, 
bears  internal  evidence  of  being  a  very  good  quantitative  study  and  favors 
an  atomic  weight  of  antimony  somewhat  less  than  122. 

1  Henz,  Z.  anorg.  attgem.  Chem.,  37,  6  (1903). 

2  Vortmann  and  Metzl,  Z,  anal.  Chem.,  44,  526  (1905). 

3  Kolb  and  Formhals,  Z.  anorg.  attgem.  Chem.,  58,  189  (1908). 

4  Hallmann,  Vergleichende  Untersuchen  ii.  Methoden.   d.  quant.    Antimonbest., 
Jnaug.  Dis.,  Aschen,  1911. 

5  Youtz,  Z.  anorg.  attgem.  Chem.,  37,  337  (1903). 

6  Beckett,  Beitrag  Best.  d.  Antimons.  Inaug.  Dis.  Zurich,  1909. 

7  Von  Bacho,  Monatsh.,  37,  106  (1916). 

8  Treadwell,  "Kurzes  Lehrbuch  anal.  Chem.,  5th  ed.,  2,  p.  563,  retained  in  the  6th  ed. 


10 

It  is  with  such  a  background  that  the  preparation  of  antimony  tri- 
bromide  was  undertaken  and  determinations  carried  out  of  the  ratios 
SbBr3  :  3Ag  and  SbBr3  :  SAgBr,  using  modern  methods  of  preparing 
the  materials  and  modern  technique  in  carrying  out  the  analytical  proc- 
esses. 

Preparation  of  Materials. 

The  preparation  of  pure  bromine  and  pure  silver  as  auxiliary  standards 
followed  methods  well  known  in  atomic  weight  work.  Separation  of 
crystals  from  mother  liquor  was  accomplished  by  centrifugal  drainage, 
and  electrical  heating  was  resorted  to  wherever  practicable. 

Pure  Bromine. — In  brief  outline  the  process  for  bromine  was  as  fol- 
lows. A  high  grade  of  commercial  bromine  was  dissolved  in  a  cone, 
solution  of  calcium  bromide  and  distilled  therefrom.  Then  the  pro- 
cedure followed  that  given  by  Baxter,  Moore  and  Boylston,1  except  that 
the  removal  of  iodine  was  accomplished  by  the  two  steps  of  boiling  off 
an  excess  of  bromine  added  in  forming  potassium  bromide  from  the  oxalate 
and  of  crystallizing  out  the  potassium  bromide  rather  than  evaporating 
the  solution  to  dryness. 

Pure  Silver. — Silver  from  students'  cyanide  analyses  was  precipitated 
with  ammonium  sulfide,  dissolved  in  nitric  acid,  precipitated  in  dil.  solu- 
tion with  hydrochloric  acid,  then  converted  to  metal  by  the  method  of 
Buckner  and  Hulett.2  The  silver  was  then  fused  in  air  on  a  pure  lime 
support  and  the  process  to  this  point  repeated.  It  was  then  carried 
through  the  later  purification  process  as  outlined  by  Baxter,  Moore  and 
Boylston,  including  formate  precipitation,  electrolytic  deposition  and 
fusion  in  electrolytic  hydrogen. 

Accessory  Reagents. — Reagents  used  in  the  analytical  work  or  inci- 
dental to  the  preparation  of  pure  bromine  and  silver  were  purified  and 
handled  with  a  care  proportional  to  the  purity  of  the  bromine  and  silver 
themselves. 

Water  was  redistilled  with  block-tin  condenser  from  alkaline  perman- 
ganate solution,  first  allowing  it  to  simmer  for  several  hours  and  then 
discarding  a  moderate  first  fraction. 

Nitric  Acid. — Ordinary  c.  P.  nitric  acid  was  treated  with  a  crystal  of 
sodium  chlorate,  then  carefully  distilled,  using  a  quartz  condenser  and 
collecting  the  middle  third.  This,  by  careful  test,  was  shown  to  be  free 
from  iron  and  chloride  and  was  preserved  by  sealing  up  in  resistance  glass 
flasks  that  had  been  thoroughly  soaked  in  the  usual  chromic  acid  clean- 
ing solution  and  then  well  rinsed  and  steamed. 

Calcium  Bromide. — A  solution  for  dissolving  the  bromine  was  prepared 
according  to  the  following  reaction.  CaCO3  +  HCOOH  +  Br2  =  CaBr2  -f- 

1  Baxter,  Moore  and  Boylston,  J.  Am.  Chem.  Soc.,  34,  259  (1912). 

2  Buckner  and  Hulett,  Trans.  Am.  Electrochem.  Soc.,  22,  372  (1912). 


11 

H2O  -f-  2C02.  A  high  grade  of  precipitated  calcium  carbonate  was 
treated  with  diluted,  redistilled  formic  acid,  using  slightly  less  than  one 
gram  molecule  of  formic  acid  to  one  of  calcium  carbonate;  then  bromine 
was  added  carefully  in  slight  excess,  and  the  solution  boiled,  filtered,  and 
evaporated  to  such  a  volume  that  it  was  nearly  saturated  with  respect 
to  calcium  bromide. 

Potassium  oxalate  was  twice  recrystallized  from  water.  In  the  final 
product  careful  tests  for  iron  and  chlorine  were  negative. 

Kahlbaum's  potassium  permanganate,  "Zur  Analyse,"  and  freshly  fumed 
sulfuric  acid  gave  negative  tests  for  halogen  and  so  were  used  directly. 

Phosphorus  pentoxide  was  sublimed  in  a  current  of  oxygen  and  found 
by  test  with  silver  ammonia  nitrate  to  be  free  from  reducing  material. 

Hydrochloric  acid  and  ammonium  hydroxide  were  purified  by  distilla- 
tion. 

Cane  sugar  was  precipitated  from  solution  by  freshly  distilled  alcohol 
and  found,  on  ignition,  to  leave  an  unweighable  residue. 

Ammonium  formate  was  prepared  by  careful  neutralization  of  formic 
acid  that  had  been  distilled  from  silver  formate. 

The  preparation  of  the  pure  lime  support  followed  essentially  the  de- 
tails given  by  Richards  and  Wells.1 

Pure  hydrogen  was  generated  by  electrolysis  of  sodium  hydroxide  solu- 
tions in  all-glass  apparatus  with  nickel  gauze  electrodes,  drying  being 
effected  by  a  long  tube  of  solid  sodium  hydroxide. 

Tartar ic  Acid. — Careful  tests  of  Kahlbaum's  chemically  pure  tartaric 
acid  showed  that  it  was  satisfactory  for  use  without  further  purification. 
Preliminary  experiments  were  undertaken  to  see  if  hydrofluoric  acid  might 
not  be  used  in  place  of  the  usual  tartaric  acid  as  a  solvent  for  the  anti- 
mony bromide.  It  was  found  that  antimony  bromide  dissolves  readily 
in  hydrofluoric  acid,  that  no  considerable  excess  of  the  acid  is  required, 
and  that  such  a  solution  may  be  diluted  largely  without  precipitation. 
But,  due  to  the  action  of  the  hydrofluoric  acid  on  the  glass,  the  solution 
underwent  slow  decomposition  with  precipitation  of  antimony  oxybro- 
mide.  Neutralization  of  the  acid  solution  failed  to  give  it  the  desired 
stability,  so  further  attempts  in  this  direction  were  abandoned  and  tar- 
taric acid  was  finally  adopted. 

Pure  Antimony. 

Purification  of  Antimony  Compounds. — Fractional  distillation  of 
antimony  bromide  as  a  means  of  separation  from  lead,  copper,  iron,  tin 
and  arsenic  was  studied,  using  a  commercial  preparation  to  which  small 
amounts  of  these  metals  were  added  separately  in  the  form  of  bromides, 
and  the  material  distilled  into  small  glass  bulbs  as  receivers.  Two  small 
1  Richards  and  Wells,  J.  Am.  Chem.  Soc.,  25,  481  (1905). 


12 

fractions  were  collected  first,  then  the  bulk  of  the  antimony  bromide 
distilled  off  and  the  residue  examined.  Lead,  copper  and  iron  were  com- 
pletely retained  in  the  distilling  flask,  while  tin  was  found  largely  in  the 
first  fraction  and  was  completely  removed  by  the  time  */4  of  the  material 
had  distilled  over.  The  method  proved  unsatisfactory  in  the  case  of 
arsenic,  positive  tests  being  obtained  on  the  residue  even  after  3/4  of  the 
antimony  bromide  had  been  discarded. 

In  the  course  of  this  work  a  modified  distilling  flask  was  developed  with 
the  receiver  attached  at  the  top  by  means  of  a  ground  glass  joint.  This 
avoided  the  usual  dead  space  which  reduces  the  effectiveness  of  separa- 
tion by  fractional  distillation. 

A  second  method  studied  for  the  purification  of  antimony  compounds 
was  the  recrystallization  of  tartar  emetic.  Using  centrifugal  drainage 
and  working  on  a  moderate  scale  it  was  found  that  small  amounts  of  cop- 
per, iron,  tin  and  arsenic,  introduced  as  chlorides — except  arsenic,  which 
was  introduced  as  dipotassium,  hydrogen,  orthoarsenate — were  rapidly 
removed  in  the  mother  liquors.  Lead,  however,  after  reduction  to  a  cer- 
tain small  value,  was  found  in  about  equal  amounts  in  successive  crops 
of  crystals. 

It  was  at  first  intended  to  use  recrystallization  of  tartar  emetic,  followed 
by  decomposition  with  heat  as  a  means  of  obtaining  the  metal,  which 
might  then  be  converted  to  the  bromide  and  subjected  to  a  process  of  frac- 
tional distillation.  At  this  time,  however,  the  work  of  Groschuff1  became 
available,  and  this  appeared  so  promising  that  further  study  on  the  diffi- 
culties of  the  suggested  method  was  abandoned. 

Kahlbaum's  antimony  trioxide2  was  dissolved  in  fairly  concentrated 
hydrochloric  acid,  filtered  through  hardened  filter  paper  and  treated  with 
chlorine  from  a  cylinder  of  the  liquefied  gas  till  oxidized  to  antimony 
pentachloride.  This  solution  was  evaporated  on  a  water-bath  until 
very  concentrated,  then  saturated  with  dry  hydrogen  chloride  (prepared 
by  dropping  cone,  hydrochloric  acid  into  cone,  sulfuric  acid  and  washing 
with  sulfuric  acid)  and  finally  cooled  to  less  than  0°.  Under  these  condi- 
tions the  compound  HSbCle-YzH^O  separates  out  in  fine  crystalline  form. 
These  crystals  were  collected  on  a  Biichner  funnel,  then  placed  in  a  porce- 
lain evaporating  dish,  a  little  water  added  and  the  dish  placed  on  the 
water-bath  until  a  clear  solution  was  obtained.  By  repeating  the  earlier 
process  a  new  crop  was  formed  which  was  drained  centrifugally  in  plat- 
inum cups  and  recrystallized  4  times.  These  crystals  were  then  worked 

1  Groschuff,  Z.  anorg.  allgem.  Chem.,  103,  164  (1918),  recommending  the  method 
of  Weinland  and  Schmid.    Ibid.  44,  43  (1905). 

2  Quantitative  analysis  of  the  trioxide  using  the  method  of  Groschuff  for  concen- 
trating impurities  revealed  the  following  impurities:     S,  0.005%;  Sn,  0.002%;  Cu, 
0.001%;  Fe,  0.015%;  Pb,  0.004%;  As,  0.001%. 


13 


up  in  separate  lots  as  follows:  they  were  dissolved  in  water,  diluted  largely 
and  heated  on  a  water-bath  to  complete  the  hydrolysis,  collected  on  a 
Buchner  funnel,  washed  copiously  with  hot  water,  then  transferred  to  an 
evaporating  dish  and  twice  evaporated  to  dryness  with  nitric  acid  to  re- 
move the  last  trace  of  chloride.  Tests  for  chlorine  on  this  material  were 
negative. 

Recovery  of  the  Metal. — Metallic  antimony  was  recovered  from  this 
preparation,  after  ignition  to  the  oxide,  in  two  ways,  (a)  heating  in  hydro- 
gen; (6)  fusing  with  sodium  cyanide. 

Preliminary  experiment  had  shown  that  antimony  oxide  may  be  satis- 
factorily reduced  to  the  metal  by  heating  in  hydrogen  providing  a  tem- 
perature is  maintained  slightly  below  the  melting  point  of  the  trioxide. 
If  the  trioxide  melts  it  becomes  coated  over  with  the  metal  in  such  a  way 
as  to  be  rather  effectively  protected  against  further  reduction.  At  the 
lower  temperature  the  reduction  proceeds  rather  slowly,  but  it  may  be 
carried  out  in  such  a  way  as  to  require  little  attention  so  that  the  time 
used  was  not  a  serious  objection.  There 
was  prepared  a  cylindrical  bomb  of  iron  (see 
Fig.  1)  about  75  mm.  deep  and  75  mm.  in 
diameter,  large  enough  to  receive  a  fair- 
sized  crucible.  A  cover  was  carefully  ground 
and  polished  so  as  to  fit  nearly  gas-tight, 
clamps  being  arranged  for  fastening  on  the 
cover,  which  was  provided  with  two  20  cm. 
lengths  of  small  iron  tubing  to  serve  as  inlet 
and  outlet  tubes.  The  outlet  tube  was  fitted 
with  a  small  hard-glass  tube  bent  so  as  to  be 
out  of  the  way  of  the  crucible  and  reaching 
nearly  to  the  bottom  of  the  bomb.  The 
inlet  tube  came  merely  to  the  lower  edge  of 
the  cover.  The  whole  fitted  nicely  into  a  pot 
furnace  wound  to  give  temperatures  ranging 
up  to  750-800°. 

The  hydrogen  used  for  the  reduction  was 
compressed  electrolytic  hydrogen.  This  was 
passed  first  through  a  long  tube  of  freshly 
heated  charcoal  to  remove  traces  of  hydro-  Fig.  1. — Apparatus  used  for  re- 
carbon;1  second,  a  glass  tube  heated  to  dull  Auction  of  antimony  oxide  in 
redness  to  convert  any  oxygen  to  water,  a  ^~gen.  i  =  inlet  tube  for 

hydrogen;    o  =  outlet  tu  b  e; 

1  Roscoe  and  Schorlemmer,  "Treatise  on  Inor-      c  =  crucible  for  antimony 
ganic  Chemistry,"  4th  ed.,  I,  p.  153.  oxide. 


14 

calcium  chloride  tube,  and  finally  through  a  phosphorus  pentoxide  tube 
for  drying. 

In  carrying  out  the  reducing  process  a  crucible  was  filled  reasonably 
full  of  the  antimony  oxide,  placed  on  a  low  triangle  in  the  bomb,  covered 
with  an  inverted  quartz  cover,  then  the  cover  fastened  on  and  the  bomb 
placed  in  the  pot  furnace.  Hydrogen  was  next  turned  on  and  finally  the 
furnace  heated  to  a  temperature  of  approximately  500°.  After  about  two 
days,  which,  under  the  conditions  as  standardized,  was  sufficient  for  a 
satisfactory  reduction  of  the  oxide  to  metal,  the  temperature  was  raised 
to  about  650°,  high  enough  to  melt  the  antimony,  and  then  the  furnace 
permitted  to  cool  down.  Bright  buttons  of  antimony  with  a  few  dark 
specks  on  the  surface  were  obtained.  The  specks  were  removed  mechan- 
ically, the  buttons  pounded  up  in  a  clean  agate  mortar  and  then  reheated 
in  hydrogen  to  400-450°  for  final  drying.  This  latter  was  done  imme- 
diately before  the  material  was  to  be  used  for  the  synthesis  of  the  tri- 
bromide. 

In  the  reduction  of  the  oxide  in  hydrogen  it  was  noticed  that  the  porce- 
lain crucible  was  blackened,  the  stain  thus  produced  not  being  removed 
by  soaking  in  nitro-hydrochloric  acid.  Consequently  contact  with 
porcelain  was  avoided  and  one  bath  of  the  oxide  was  reduced  to  metal 
using  a  quartz  crucible,  and  another  was  reduced  on  a  support  of  pure 
lime  similar  to  that  used  in  the  preparation  of  pure  silver.  In  the  second 
case  the  support,  for  obvious  reasons,  underwent  considerable  disinte- 
gration; but,  nevertheless,  effectively  kept  the  antimony  from  contact 
with  the  crucible.  The  two  specimens  of  antimony  were  labelled,  respec- 
tively, Preparations  I  and  II. 

For  the  second  method  of  reducing  the  oxide  a  high  grade  commercial 
sodium  cyanide  was  recrystallized  4  times  from  water  using  centrifugal 
drainage,  and  dried  over  sodium  hydroxide.  The  resulting  material  was 
free  from  iron  and  chloride.  This  was  mixed  intimately  with  the  oxide  in 
a  tall  porcelain  beaker,  then  heated  in  the  electric  furnace  for  several 
hours  at  slightly  above  the  melting  point  of  antimony.  After  cooling, 
the  button  of  antimony  was  cleaned  mechanically,  fused  in  hydrogen,  then 
pounded  up  in  an  agate  mortar  and  dried  in  hydrogen  when  needed. 

Antimony  Bromide. 

Construction  of  Apparatus. — The  attempt  to  prepare  antimony  bro- 
mide in  such  a  way  as  to  use  the  Harvard  bottling  method  was  soon  aban- 
doned, because  the  volatility  of  this  compound  when  slightly  above  its 
melting  point  and  its  hygroscopic  character  both  make  fusion  in  an  atmos- 
phere of  dry  hydrogen  bromide  a  method  of  doubtful  value  for  the  con- 
version of  traces  of  oxide  or  oxybromide  to  bromide.  To  test  this  point 
a  sample  of  antimony  bromide  was  moistened  slightly,  then  treated  for 
several  hours  at  just  above  the  melting  point  with  hydrogen  bromide. 


15 

On  distilling  off  the  antimony  bromide  the  residue  left  was  distinctly 
greater  than  that  given  by  another  portion  of  the  dry  bromide  distilled 
directly. 

The  next  attempt  was  in  the  direction  followed  by  Baxter.  Moore, 
and  Boylston,1  in  the  work  on  phosphorus,  involving  preparation  of  the 
tribromide,  fractional  distillation,  and  collection  of  the  middle  portion 
in  a  series  of  sampling  bulbs — all  in  an  inert  atmosphere  in  all-glass  ap- 
paratus. The  first  construction  followed  their  general  design,  except 
that  a  separate  bulb  was  added  at  the  beginning  from  which  the  bromine 
could  be  distilled  on  to  the  antimony,  and  the  preparation  chamber  con- 
sisted of  an  inclined  tube  lying  in  an  aluminum  block  oven,2  keeping  the 
antimony  bromide  molten  and  drained  off  and  exposing  fresh  surface 
of  metal  to  the  action  of  the  bromine. 

Vacuum  was  obtained  at  first  by  a  Cenco-Nelson  2-phase  pump,  later 
replaced  by  the  "Hyvac,"  an  oil-immersed  pump  capable  of  maintain- 
ing a  vacuum  of  0 . 003  mm. 

Nitrogen  for  drying  the  apparatus  and  for  establishing  an  inert  atmos- 
phere was  prepared  from  commercial  compressed  nitrogen  containing 
0.5%  oxygen.  The  removal  of  oxygen  by  the  method  described  by 
Badger3  was  discarded  when  it  was  observed  that  the  resulting  gas  had  a 
slight  reducing  action.  Instead  the  oxygen  was  absorbed  by  copper  turn- 
ings heated  to  a  dull  red.  The  purifying  and  drying  train  was  completed 
by  a  60  cm.  tube  of  soda  lime,  3  Emmerling  towers  of  sulfuric  acid  and  a 
tower  of  phosphorus  pentoxide.  No  reducing  effect  was  noted  in  the  gas 
thus  obtained  and  careful  test  showed  it  to  be  free  from  oxygen. 

During  the  course  of  preliminary  runs  to  get  acquainted  with  both  the 
apparatus  and  the  process,  certain  mechanical  difficulties  were  encoun- 
tered with  the  trap  arrangement  used  in  discarding  the  first  fraction  of 
the  distillate.  On  due  consideration  it  was  felt  that  first  fractions  could 
be  discarded  nearly  as  effectively  by  setting  aside  the  first  2  or  3  bulbs 
into  which  material  was  condensed,  and  further,  that  with  antimony 
and  bromine  carefully  purified  the  chief  danger  was  from  moisture,  which 
could  be  avoided  better  by  proper  drying  precautions  than  by  discarding 
a  special  fraction.  Therefore  the  trap  and  separate  series  of  discard 
bulbs  were  omitted.  At  the  same  time  there  were  added  at  the  other 
end  of  the  sampling  bulbs  2  U-tubes,  one  containing  metallic  antimony, 
which,  at  100°,  effectively  absorbed  any  traces  of  bromine  that  were  car- 
ried past  the  preparation  chamber,  the  second,  phosphorus  pentoxide  to 
ensure  complete  drying  of  any  gases  which  might  come  into  the  bulbs 
from  that  direction. 

1  Loc.  cit. 

2  Baxter  and  Tilley,  J.  Am.  Chem.  Soc.,  31,  206  (1909). 
«  Badger,  /.  Ind.  Eng.  Ghent.,  n,  1052  (1919). 


16 


In  one  of  the  earlier  experiments  it  was  discovered,  on  sealing  off  an 
empty  bulb  with  a  full  one  and  distilling  the  antimony  bromide  out  of  the 
latter,  that  the  residue  left  was  unexpectedly  large.  To  study  this  further, 
a  sample  of  antimony  bromide  was  moistened  with  a  drop  of  water,  then 
placed  in  the  first  of  a  series  of  10  well-dried  bulbs,  the  system  evacuated 
and  sealed,  and  the  material  distilled  from  one  bulb  to  the  next,  sealing 
off  each  residue  as  obtained.  The  residues  decreased  in  amount  but 
were  fairly  marked  in  the  first  three  bulbs. 

Cooke  had  suggested  the  possibility  of  any  oxychloride  of  antimony 
distilling  over  in  part  with  the  chloride.  It  seemed  as  if  something  of 
that  sort  might  be  the  case  here.  The  following  experiment,  however, 
pointed  to  moisture  as  being  the  probable  source  of  the  residues.  Phos- 
phorus pentoxide  was  added  to  some  antimony  bromide  and  the  above 
study  repeated.  In  the  first  distillation  some  chemical  reaction  took 
place,  but  in  the  second  bulb  there  was  no  visible  residue.  From  this  time 
on  the  drying  temperature  was  raised  to  at  least  250°  and  the  time  ex- 
tended to  a  minimum  of  24  hours.  With  these  precautions  the  amount 
of  residue  became  uniformly  slight.  In  two  cases  distilling  off  4  or  5  g. 
of  antimony  bromide  left  0.09  mg.  and  0.08  mg.,  respectively,  approxi- 
mately 0.002%.  For  comparison,  Cooke's  residues  from  the  bromide 
averaged  0.028%,  even  though  he  maintained  a  high  enough  tempera- 
ture to  feel  justified  in  assigning  the  formula  Sb4O5Br2  to  the  residue. 


Fig.  2. — Apparatus  used  for  preparation  of  antimony  bromide. 

The  apparatus  as  finally  developed  is  represented  semi-diagrammatically 
in  Fig.  2.  Heating  arrangements  were  provided  to  give  temperatures 
up  to  300°.  The  bromine  bulb  and  connecting  tubes  were  heated  with 
the  Bunsen  flame.  The  sampling  bulbs  and  antimony  U-tube  were  sus- 


17 

pended  in  a  movable  asbestos  trough  on  the  bottom  of  which  lay  a  close 
coil  of  nichrome  wire. 

Preparation  of  Samples. — Next  was  prepared  a  preliminary  series  of 
bulbs  to  study  the  analytical  process,  using  for  this  purpose  Kahlbaum's 
metallic  antimony  and  a  good  grade  of  bromine  which  had  been  distilled 
from  calcium  bromide  solution  and  dried,  first  with  sulfuric  acid,  and  finally 
with  phosphorus  pentoxide.  The  manipulation  as  finally  used  in  the 
preparation  may  well  be  given  in  some  detail.  With  the  different  parts 
of  the  apparatus  cleaned,  dried  and  sealed  together,  leaving  a  small  drop- 
ping funnel  attached  to  the  bromine  bulb  and  an  open  tube  at  the  upper 
end  of  the  preparation  tube  for  the  introduction  of  antimony,  the  appa- 
ratus was  heated  to  approximately  300°  while  a  current  of  dry  nitrogen 
was  passed  through  it  for  24  to  36  hours.  The  preparation  tube  was  then 
allowed  to  cool,  powdered  metallic  antimony — freshly  dried  and  cooled 
in  hydrogen — was  poured  into  the  preparation  chamber  and  the  inlet 
tube  sealed  off.  The  heating  was  continued  for  several  hours  longer, 
then  the  preparation  tube  cooled  to  120-130°,  the  sampling  bulbs  and 
antimony  U-tube  reduced  similarly  and  the  bromine  bulb  cooled  to  room 
temperature.  With  the  stopcock  of  the  dropping  funnel  closed  and  a 
steady  stream  of  nitrogen  maintained,  one  of  the  stopcocks  was  opened 
to  the  air  so  as  to  obtain  atmospheric  pressure  in  the  apparatus.  Then 
a  little  phosphorus  pentoxide  was  placed  in  the  dropping  funnel  and  an 
amount  of  dry  bromine  run  in  such  as  would  leave  several  grams  of  anti- 
mony unacted  upon.  Avoiding  introduction  of  air,  the  bromine  was  run 
into  the  bulb  and  the  dropping  funnel  sealed  off.  Next  a  large  beaker 
of  water  was  raised  under  the  bromine  bulb  until  the  latter  dipped  well 
into  the  water  and  heat  applied  till  a  temperature  of  50°  to  55°  was  ob- 
tained. This  distilled  the  bromine  slowly  enough  so  that  it  was  quite 
fully  taken  up  by  the  antimony,  only  traces  getting  into  the  next  por- 
tion of  the  apparatus  during  the  latter  part  of  the  operation.  When 
the  distillation  was  started  the  stopcock  leading  to  the  air  was  closed, 
the  nitrogen  shut  off  and  the  process  carried  on  at  ordinary  pressure  in 
nitrogen.  With  20  to  25  g.  of  antimony  and  10  to  12  cc.  of  bromine,  it 
required  10  to  15  hours  for  the  synthesis  of  the  antimony  bromide.  The 
bromine  bulb  was  then  sealed  off,  the  temperature  raised  to  150-160° 
and  the  materials  allowed  to  digest  for  8  to  12  hours  longer.  In  this 
way  all  trace  of  bromine  color  disappeared  and  the  melted  antimony  bro- 
mide became  light  amber-colored.  Occasionally  slight  evidence  of  action 
in  the  antimony  U-tube  was  observed;  frequently  none  was  visible. 

The  preparation  tube  was  next  cooled  to  130-140°,  the  distilling  flask, 
sampling  bulbs  and  U-tube  kept  at  about  100°  and  the  apparatus  then 
evacuated  until  the  antimony  bromide  started  to  distil  over  into  the 
flask.  The  heating  trough  was  then  permitted  to  cool  down  while  the 


18 

bulk  of  the  antimony  bromide  was  distilled  out  of  the  preparation  tube. 
Nitrogen  was  then  carefully  admitted  to  stop  the  process  and  to  lessen 
the  chance  for  accident  when  the  preparation  tube  was  sealed  off.  With 
the  latter  done,  the  apparatus  was  again  evacuated  and  heat  applied 
until  the  antimony  bromide  had  largely  distilled  into  the  first  bulb  of  the 
chain.  The  distilling  flask  was  then  sealed  off,  the  apparatus  evacuated 
to  a  pressure  of  about  1  mm. — until  the  antimony  bromide,  slightly  above 
the  melting  point,  showed  signs  of  distilling — and  then  the  series  of  bulbs 
sealed  off  from  the  antimony  U-tube.  This  left  the  bulbs  as  a  single 
unit  which  could  now  be  suspended  in  the  heating  trough  and  easily 
shifted  along  to  cool  the  bulbs  successively,  starting  at  the  end  opposite 
the  one  containing  the  antimony  bromide.  Thus,  as  the  material  was 
distilled,  successive  fractions  were  obtained,  and  practice  made  it  possi- 
ble to  regulate  the  size  of  these  fractions  in  a  satisfactory  way. 

Further  preparations  of  antimony  bromide  included  two  final  series 
using  pure  bromine  and  antimony  reduced  from  the  oxide  by  hydrogen, 
and  one  final  series  using  pure  bromine  and  antimony  reduced  from  the 
oxide  by  fusion  with  sodium  cyanide. 

In  using  Preparations  I  and  II  of  antimony  by  hydrogen,  it  was  noticed 
that  the  residues  in  the  preparation  tube  after  distilling  off  the  bromide 
were  quite  different.  The  one  from  antimony  reduced  in  quartz  was 
bright  and  clean,  the  other,  where  the  oxide  had  been  reduced  on  a  lime 
support,  being  contaminated  with  a  brownish  amorphous  substance. 
The  preparations  of  the  bromide,  however,  were  both  highly  lustrous 
white  products  of  identical  appearance.  They  constituted  the  material 
for  Series  B  and  Series  D,  respectively. 

In  the  first  preparation  of  bromide  from  metal  reduced  by  cyanide,  it 
was  found  that  the  final  material  had  a  brown  tinge.  With  the  series  of 
bulbs  still  intact  the  material  was  melted  and  poured  back  into  the  large 
bulb  and  the  distillation  repeated.  The  distillate  was  visibly  lighter  in 
color  and  a  black  residue  was  left  in  the  bulb.  This  process  was  repeated 
several  times  until  no  further  improvement  could  be  noticed.  The  ma- 
terial still  having  a  faint  straw  color,  the  small  bulbs  were  sealed  off  in 
groups  of  two.  The  bulbs  were  warmed  and  the  antimony  bromide 
poured  into  one  of  them  from  which  about  2/s  was  distilled  back  into  the 
other.  The  residue  was  distinctly  dark  in  color.  The  final  distillate 
not  being  entirely  white,  it  was  not  regarded  as  satisfactory  for  final 
analysis. 

Another  preparation  was  made  from  the  same  antimony,  except  that 
the  metal  was  first  kept  melted  for  several  hours  in  a  current  of  hydrogen, 
with  the  thought  that  this  might  remove,  or  render  harmless,  impuri- 
ties evidently  derived  from  the  cyanide  fusion.  It  may  be  noted,  paren- 
thetically, that  the  usual  method  of  purifying  metallic  antimony,  follow- 


19 

ing  fusion  of  the  oxide  with  sodium  cyanide,  is  to  maintain  the  antimony 
molten  for  a  period  of  many  hours  under  a  layer  of  the  oxide.  This  was 
purposely  omitted  here  since  it  was  desired  to  keep  the  material  as  free 
from  oxide  as  possible  and  it  is  not  improbable  that  metallic  antimony 
dissolves  the  oxide  to  some  slight  extent.  The  antimony  bromide 
prepared  from  this  batch  of  metal  was  better  than  the  previous  lot,  but 
it  still  showed  a  faint  color  even  after  repeated  redistillation. 

The  next  attempt — the  last  which  could  be  tried  without  repeating  the 
earlier  process  of  purifying  antimony — added  the  further  precaution  of 
digesting  the  antimony  bromide  in  the  preparation  tube  for  several  hours 
at  only  slightly  below  the  boiling  point  under  atmospheric  pressure,  a 
temperature  at  least  75°  higher  than  formerly  used,  or  than  is  needed 
for  any  subsequent  distillation.  It  was  felt  that  in  this  way  a  decom- 
position of  the  objectionable  impurity  might  be  accomplished  in  such  a 
way  that  gaseous  products  might  still  be  gotten  rid  of  and  non-volatile 
products  retained  in  the  earlier  residues.  These  hopes  were  rewarded  by 
obtaining  a  series  of  samples  barely  distinguishable  from  those  of  Series 
B  and  D ;  so  these  were  labelled  Series  C  and  used  for  final  analysis. 
Analysis  of  Antimony  Bromide. 

With  the  materials  thus  at  hand,  there  was  started  a  study  of  the  usual 
volumetric  determination  of  the  ratio  of  antimony  bromide  to  silver, 
using  the  nephelometric  end-point,  and,  further,  of  the  gravimetric  de- 
termination of  the  ratio  of  antimony  bromide  to  silver  bromide. 

Balance  and  Weighing. — The  balance  used  was  a  new  Troemner  No. 
10,  easily  sensitive  to  0.02  milligram.  The  weights  were  a  set  of  gold- 
plated  brass  weights  with  platinum  fractionals,  calibrated  by  the  Bureau 
of  Standards,  and  carefully  rechecked  with  one  another,  using  the  Har- 
vard method.  By  the  method  of  counterpoises  and  substitution  it  was 
easily  possible  to  check  ordinary  weights  to  within  0.02  mg.,  and,  even 
with  a  glass  vacuum  weighing  bottle  of  approximately  50  cc.  external 
volume  and  weighing  slightly  over  50  g.,  extreme  errors  did  not  exceed 
0.05  mg.  for  individual  weighings.  A  small  amount  of  radium  bromide 
was  kept  in  the  balance  case  to  prevent  the  objects  weighed  from  retain- 
ing electric  charges.1 

Vacuum  corrections  were  applied,  using  the  following  table,  based  on 
average  conditions  of  temperature  and  pressure  (density  of  air  = 
0. 001173  g.). 

Table  of  Corrections. 

Substance.  Mg.  per  gram. 

Silver —0.0285 

Silver  bromide +0 . 041 

Glass +0.332 

Sample  in  bulb — 0. 140 

1  Baxter  and  Tilley,  /.  Am.  Chem.  Soc.,  31,  212  (1909). 


20 

For  the  determination  of  the  density  of  brass  weights  used  and  of  the 
glass  from  which  the  bulbs  were  blown,  as  well  as  to  avoid  determining 
the  volume  of  each  individual  bulb,  a  weighing  bottle1  with  well  polished 
and  tightly  fitting  cap,  and  with  stopcock  attachment  for  vacuum  con- 
nection, was  used.  By  placing  object  and  evacuated  weighing  bottle  on 
the  balance  pan  and  comparing  with  a  counterpoise  similar  in  material 
and  size,  a  certain  difference  in  weight  was  obtained.  By  placing  the  ob- 
ject in  the  weighing  bottle,  evacuating,  and  comparing  again  with  the 
counterpoise  a  certain  other  difference  in  weight  was  obtained,  the  varia- 
tion representing  the  buoyant  effect  of  the  air.  By  observing  the  tem- 
perature and  pressure  at  the  time,  the  volume  of  the  object  could  be  cal- 
culated and  the  density  of  the  material  determined.  In  the  case  of  the 
samples  of  antimony  bromide  only  the  direct  weighing  in  vacua  was  needed 
since  this  made  it  unnecessary  to  apply  a  correction  for  buoyancy  of  the 
air,  other  than  that  exerted  on  the  brass  weights.  The  weight  was  ob- 
viously obtained  by  comparing  the  evacuated  weighing  bottle  empty 
with  the  evacuated  weighing  bottle  containing  the  sample  and  subtract- 
ing from  this  the  vacuum  correction  for  the  weights  used. 

As  evidence  of  the  accuracy  with  which  the  weight  in  vacua  may  thus 
be  determined  a  piece  of  glass  rod  was  weighed  in  air,  its  volume  deter- 
mined by  displacement  of  water  and  a  vacuum  correction  calculated,  the 
weight  thus  found  being  compared  with  that  obtained  by  the  method 
outlined. 

(a)     Apparent  weight  in  air 3. 17303  g. 

Vacuum  correction +0 . 00105 


Weight  in  vacuo 3. 17408 

(6)     Direct  weighing  in  vacuo  wts 3 . 17448  g. 

Correction..  —0.00044 


Weight  in  vacuo 3 . 17404 

The  weight  of  the  sample  in  the  bulb  having  been  obtained,  the  bulb 
was  placed  in  a  tall,  narrow,  thick-walled  beaker  and  covered  with  a  freshly 
prepared  and  filtered  solution  of  tartaric  acid,  allowing  3  to  4  g.  of  acid 
for  each  estimated  gram  of  antimony  bromide.  Using  a  heavy  platinum 
rod,  the  bulb  was  then  broken,  the  rod  thoroughly  rinsed  and  removed, 
and  the  solution  allowed  to  stand  with  frequent  agitation  until  all  of  the 
antimony  bromide  had  dissolved,  an  additional  time  of  6  to  12  hours 
being  allowed  to  complete  solution.  The  broken  glass  was  then  filtered 
out,  being  washed  3  times  by  decantation  with  dil.  tartaric  acid  solution 
and  then  10  to  12  times  with  water  before  transferring  to  the  filter. 
Following  ignition  and  cooling,  the  weight  of  the  glass  was  found  and  this 
subtracted,  after  correction  to  vacuum,  from  the  weight  given,  to  obtain 
1  Renard  and  Guye,  /.  chim.  phys.,  14,  57  seq.  (1916). 


21 

the  weight  of  the  antimony  bromide.  The  empty  space  in  the  bulb 
introduced  no  appreciable  error,  since  the  bulbs  were  well  evacuated. 

The  use  of  filter  paper  to  retain  the  glass,  with  correction  after  ig- 
nition for  the  ash  of  the  paper,  was  given  up  when  it  was  found  that  the 
ash  of  a  single  9  cm.  paper  of  one  brand  of  "ashless"  filters  might  run  as 
high  as  0.4  nig.,  that  even  with  the  best  grades  the  ash  of  papers  from 
different  parts  of  the  package  might  vary  as  much  as  0.05  mg.,  and  that 
there  was  no  obvious  relation  between  the  weight  of  the  filter  paper  and 
that  of  the  ash. 

A  platinum-sponge  filtering  crucible  was  next  tried  and  found  entirely 
satisfactory.  With  reasonable  attention  to  the  conditions  of  drying 
the  crucible  before  and  after  filtering,  it  was  found  possible  to  check  its 
weight  regularly  to  within  0.02  mg.  When  the  crucible  became  clogged 
with  the  fine  glass  particles  it  was  easily  cleaned  by  soaking  in  hydro- 
fluoric and  nitric  acids,  followed  by  washing  with  hydrofluoric  acid  and 
then  copiously  with  water. 

Methods  of  Analysis. — With  the  weight  of  the  samples  known,  the 
usual  Harvard  refinements1  on  the  method  of  Pelouze  were  carried  out. 
Assuming  a  value  for  the  atomic  weight  of  antimony,  an  amount  of  silver 
was  weighed  out  corresponding  to  slightly  less  than  the  sample  under 
examination.  This  was  dissolved  in  pure  dil.  nitric  acid  in  Jena  Brlen- 
meyer  flasks  provided  with  refluxing  bulbs,  the  reaction  being  carried  out 
slowly,  and  the  temperature  being  raised  finally  to  remove  the  nitrous 
fumes. 

In  filtering  out  the  glass,  the  filtrate  had  been  collected  in  3-liter  Erlen- 
meyer  precipitation  flasks  provided  with  well-polished  glass  stoppers. 
To  the  solution,  diluted  to  about  0 . 1  N  concentration  with  respect  to 
bromide  ion,  was  added  the  silver  nitrate  solution,  carrying  out  this 
operation  at  night  under  red  light.  All  processes  of  transfer  of  materials, 
filtering  and  washing,  taking  test  portions,  etc.,  involved  in  the  analysis 
of  the  samples,  took  place  under  the  cover  of  a  large  sheet  of  glass  fastened 
over  the  desk  adjacent  to  a  vertical  pane  which  diminished  drafts  from  the 
side. 

With  the  silver  nitrate  solution  added,  the  flask  was  warmed  slightly 
by  the  hands,  then  the  stopper  inserted,  and  the  flask  shaken  vigorously 
for  several  minutes.  It  was  then  wrapped  carefully  in  a  black  cloth  as 
protection  from  the  light  during  the  day.  The  solution  was  shaken  oc- 
casionally during  36  hours  and  permitted  to  settle  for  10  to  12  hours, 
then  samples  were  taken  for  nephelometric  examination.  According  to 
the  conditions  observed,  dilute  standard  solutions  of  silver  nitrate  and 
of  potassium  bromide  were  used  to  make  up  any  slight  deficiency  of  silver 
or  bromide  ion.  The  shaking  process  was  repeated  and  the  solution 
1  Described  in  detail  by  Richards  and  Wells.  /.  Am.  Chem.  Soc.,  27,  502  seq.  (1905). 


22 

again  tested  2  days  later.  With  equivalence  of  silver  to  bromide  finally 
obtained — a  condition  in  which  2  equal  portions  of  the  solution  develop 
equal  opalescence  when  treated  with  equivalent  excess  of  silver  nitrate 
and  potassium  bromide,  respectively — corrections  were  applied  for  all 
adjustments  required,  including  material  removed  in  the  sampling,  and 
weights  were  obtained  representing  the  ratio  SbBr3  :  3Ag. 

To  the  above  solution  was  then  added  about  50  cc.  of  0. 1  N  silver  ni- 
trate solution.  The  flask  was  shaken  for  a  short  time  and  allowed  to  stand 
for  3  or  4  days  with  occasional  agitation.  The  clear  solution  was  then 
poured  through  a  platinum-sponge  filtering  crucible,  the  precipitate  of  sil- 
ver bromide  washed  15  times  with  approximately  1%  nitric  acid  and 
finally  transferred  to  the  crucible  with  this  same  solution  under  hydro- 
static pressure.  After  rinsing  twice  with  water,  the  precipitate  was  dried 
overnight  at  180°,  cooled  and  weighed.  The  bulk  of  the  precipitate  was 
transferred  to  a  quartz  crucible,  weighed,  fused  with  cover  on  in  an  elec- 
tric furnace,  cooled  and  reweighed,  and  the  loss  on  fusion  calculated  to 
the  basis  of  the  total  weight  of  dried  silver  bromide.  The  crucible  in 
which  the  silver  bromide  had  been  dried  was  conveniently  cleaned  by 
treatment  with  powdered  zinc  in  slightly  acid  water,  then  rinsed  thor- 
oughly, and  treated  successively  with  nitric  acid,  and  ammonium  hy- 
droxide. It  was  then  washed  copiously  and  dried.  Meanwhile  the 
precipitation  flask  was  treated  with  25  cm.  of  ammonium  hydroxide, 
allowed  to  stand  overnight,  then  rinsed  out,  the  rinsings  being  diluted 
to  a  known  volume  and  tested  for  silver  ion  by  comparison  with  a  standard 
similarly  prepared.  A  correction  for  silver  bromide  in  the  flask  was  thus 
obtained.  The  weight  of  the  silver  bromide,  with  proper  correction  for 
material  retained  in  the  precipitation  flask,  for  loss  on  fusion,  and  for  ad- 
justments of  the  solution  in  the  volumetric  determination  gave  a  basis  for 
calculating  the  ratio  SbBr3  :  3AgBr. 

Preliminary  Studies. — Using  the  introductory  preparation  of  anti- 
mony bromide  derived  from  Kahlbaum's  antimony,  the  above  analytical 
process  was  studied.  This  series  of  bulbs  had  totaled  7,  so,  discarding 
the  first  and  last,  there  were  5  bulbs  representing  in  numerical  order  the 
middle  portion  of  the  preparation. 

The  volumetric  determination  ran  smoothly  after  it  had  been  found  by 
experience  that  an  external  standard  had  to  be  set  up  to  determine  with 
reasonable  accuracy  the  concentration  of  bromide  ion  in  the  solution. 
The  use  of  such  external  standard  was  adopted  at  the  start  in  accordance 
with  general  practice.1  But  the  idea  suggested  itself  that  there  is  an 
inevitable  error  in  adjusting  concentrations  of  the  various  materials  in 
such  a  way  as  to  duplicate  the  conditions  present  in  the  solution  being 
examined.  And  as  a  means  of  avoiding  such  error  it  seemed  feasible  to 
1  Richards  and  Wells,  Am.  Chem.  J.,  31,  242  (1904);  Richards,  ibid.,  35,  512  (1906)- 


23 

take  two  portions  of  the  solution,  treating  one  with  silver  nitrate  and  the 
other  with  an  equivalent  amount  of  potassium  bromide  and  then  match 
opalescence  by  adding  to  the  weaker  one  sufficient  silver  ion  or  bromide 
ion  as  the  case  might  be.  Then  if  the  original  solution  showed  deficiency 
of  silver  ion  the  amount  of  silver  ion  added  to  the  tube  containing  potas- 
sium bromide  in  matching  the  other  tube  would  give  a  basis  for  estimating 
how  much  silver  ion  should  be  added  to  the  solution  in  the  flask.  That 
this  scheme  did  not  work  may  be  seen  in  the  following  data  concerning  one 
of  the  determinations. 

SUCCESSIVE  ADDITIONS  OF  SILVER  ION  CORRESPONDING  TO  INDICATIONS  IN 
TEST  SOLUTIONS. 

Date. 

2-19-20 +0.40  mg.  Ag 

2-24-20 +0.40 

,2-27-20 +0.40 

3-2-20 +0.20 

3-^4-20 equilibrium 

In  attempting  to  account  for  this  unexpected  behavior,  a  brief  study 
of  the  effect  of  tartaric  acid  on  the  determination  of  silver  ion  and  of 
bromide  ion  was  undertaken.  The  results  may  be  summarized  as  fol- 
lows. Tartaric  acid  does  not  affect  appreciably  the  determination  of 
small  amounts  of  silver  ion.  It  does,  however,  affect  the  determination 
of  small  amounts  of  bromide  ion,  the  effect,  strangely  enotfgh,  decreasing 
with  decreasing  concentration  of  bromide  ion.  So,  while  the  above 
scheme  did  not  work  satisfactorily  for  the  determination  of  bromide  in 
amounts  ranging  over  0 . 25-0 . 30  mg.  per  liter,  yet  for  the  lower  concen- 
trations corresponding  to  a  saturated  solution  of  silver  bromide  the 
nephelometric  end-point  was  shown  to  be  reasonably  accurate. 

The  volumetric  data  on  the  preliminary  series  is  given  in  the  following 
table,  the  bulbs  being  analyzed  in  the  order  in  which  they  were  collected. 

TABLE   I. — ANALYSES   OP   ANTIMONY   TRIBROMIDE   FROM   KAHLBAUM'S   ANTIMONY. 

Wt.  sample.  Wt.  silver.  Ratio  SbBr:3Ag.    At.  wt.  antimony. 

1 2.54052  2.27493  1.11675  121.675 

II 3.86859  3.46507  1.11645  121.577 

III 4.07278  3.64722  1.11668  121.651 

IV 3.80772  3.40997  1.11664  121.638 

V...  4.72332  4.23070  1.11644  121.574 


Average     1.11663  121.623 

The  atomic  weight  of  antimony  is  calculated  on  the  basis  of  Ag  = 
107.880,  using  Baxter's  ratio  Ag  :  AgBr  =  0.574451  as  an  intermediate 
step. 

The  gravimetric  determinations  of  the  antimony  ratio  in  the  preliminary 
series  were  all  unsatisfactory  for  various  causes  which  were  systematically 
1  Baxter,  J.  Am.  Chem.  Soc  28,  1322  (1906). 


24 

eliminated.  In  earlier  analyses,  black  spots  in  the  fused  silver  bromide 
frequently  showed  inaccuracy  in  the  composition  of  the  precipitate, 
and  heating  such  a  precipitate  in  chlorine  to  convert  any  silver  bromide 
and  metallic  silver  to  silver  chloride  gave  variable  results  indicating  the 
presence  of  small  amounts  of  other  volatile  material,  probably  antimony 
compounds. 

With  errors  in  manipulation  corrected,  it  seemed  desirable  to  test  the 
method  and  gain  additional  experience  by  carrying  out  a  few  analyses 
on  material  of  known  composition.  For  this  purpose  some  of  the  potas- 
sium bromide  was  used  that  had  been  prepared  in  one  of  the  last  steps  of 
purifying  bromine.  A  sample  was  dried  by  fusing  in  platinum,  then  dis- 
solved in  water,  diluted  to  one  liter,  and  a  solution  of  15  g.  of  tartaric 
acid  added.  Then  the  usual  determinations  of  the  ratios,  potassium 
bromide  to  silver  and  potassium  bromide  to  silver  bromide  were  carried 
out.  The  results  follow. 

Wt.    KBr  =  6.01916;   Wt.    Ag  =  5.45519;   Wt.    AgBr  =  9.49639.     Ratio   KBr' 
Ag  =  1.10336;     Ratio  KBr  :  AgBr  =  0.63387.     Ratio  Ag  :  AgBr  =  0.57445. 

By  comparion  with  the  following  ratios  by  Richards  and  Mueller,1 


—  -  =  1.10319;  =Z     =  0.63373;  and  with  the  ratio  by  Baxter,  Ag  : 
Ag  AgBr 

AgBr  =  0.57445,  it  may  be  seen  that  the  material  contained  slightly 
less  than  the  required  amount  of  bromine,  unless,  indeed,  the  tartaric  acid 
present  was  preventing  an  accurate  determination  of  bromide  by  either 
the  volumetric  or  the  gravimetric  method.  Also  the  ratio  of  silver  re- 
quired to  silver  bromide  obtained  checked  exactly  that  obtained  by  Bax- 
ter in  determining  the  atomic  weight  of  bromine.  The  fused  silver  bro- 
mide was  a  clear  amber-colored  mass. 

To  check  up  still  more  closely  the  possible  effect  of  tartaric  acid  two 
more  of  the  volumetric  determinations  were  carried  out  on  potassium 
bromide,  tartaric  acid  being  present  in  one  case  and  absent  in  the  other. 
The  samples  were  dried  first  by  fusion  in  nitrogen. 

1.  2. 

Tartaric  acid  absent.  Tartaric  acid  present. 

Wt.  KBr  ..................     3.34853  3.54828 

Wt.  silver  .................     3.03532  3.21617 

Ratio  KBr/Ag  .............     1.10319  1.10326 

Wt.  AgBr  ........................  5.59914 

Ratio  KBr/AgBr  ..................  0.63372" 

Ratio  Ag/AgBr  ...................  0.57440 

a  Fused  AgBr  not  clear. 

In  the  case  of  No.  1  a  slight  mechanical  loss  of  silver  bromide  spoiled 
the   gravimetric  determination,  but  the  silver  bromide  was  nevertheless 
dried  and  fused  in  quartz  to  determine  its  appearance.     As  a  further  check 
1  Richards  and  Mueller,  /.  Am.  Chem.  Soc.,  29,  652,  654  (1907). 


25 

on  the  purity  of  the  amber  mass  the  silver  bromide  was  then  fused  in 
chlorine. 

Wt.  silver  bromide 5.01673 

Wt.  final  residue 3 .82902 

Ratio 1.31019 

Correct  ratio  AgBr  :  AgCl 1 .31018  (determined  by  Baxter) 

The  exact  agreement  of  the  volumetric  ratio  with  that  of  Richards 
and  Mueller  may  have  been  somewhat  fortuitous,  but  the  data  have  dis- 
tinct bearing  on  the  purity  of  the  silver.  The  close  check  of  the  ratio 
of  silver  bromide  to  silver  chloride  with  that  of  Baxter,  favored  as  it  is  by 
the  fact  that  no  transfer  of  material  is  involved  in  its  determination, 
gives  evidence  of  the  purity  of  the  silver  bromide. 

Furthermore,  it  appears  from  No.  2  that  there  may  be  some  slight 
effect  of  tartaric  acid  in  rendering  the  determination  of  bromide  inexact, 
though  the  material  was  not  prepared  and  handled  throughout  with  the 
care  required  to  assign  positive  significance  to  the  difference  between 
the  two  ratios  1.10326  and  1.10319,  which  vary  from  each  other  by 
less  than  7  parts  in  100,000.  Nor  is  there  the  concordant  series  of  analyses 
that  would  be  required  to  establish  such  a  difference.  At  its  maximum, 
assigning  full  weight  to  the  earlier  determination  where  less  care  was 
taken  to  protect  the  material  during  the  drying  process,  the  error  would 
not  be  over  1  part  in  10,000. 

Qualitative  testing  of  dilute  bromide  solutions  in  the  nephelometer 
failed  to  reveal  corroborating  data. 

It  is  of  interest  that  in  recent  work  on  the  atomic  weight  of  tin1  in  which 
the  chloride  and  the  bromide  were  prepared  and  analyzed  by  methods 
similar  in  principle  to  the  one  here  used,  mention  is  made  of  the  possi- 
bility of  interference  due  to  tartaric  acid,  but  it  is  dismissed  as  improba- 
ble. The  close  agreement  of  the  work  of  Brauner  and  Krepelka  and  that 
of  Briscoe  with  that  of  Baxter  and  Starkweather2  establishes  the  fact 
that  any  error  from  such  source  must  be  very  small. 

Since  a  further  testing  out  of  this  point  would  need  to  be  supplemented 
by  a  series  of  tests  concerning  the  possible  influence  of  antimony  on  the 
nephelometric  end-point  if  experimental  completeness  were  to  be  attained, 
while  the  error  in  the  accepted  atomic  weight  of  antimony  is  of  gross 
rather  than  microscopic  magnitude,  it  seemed  not  illogical  to  leave  such 
refinements  for  later  study. 

Concerning  the  gravimetric  determination  of  the  ratio  of  potassium 
bromide  to  silver  bromide  in  the  presence  of  tartaric  acid,  it  may  be  noted 
that  the  numercial  value  checks  Mueller's  work  closely,  but  the  fused  mass 

1  Briscoe,  /.  Chem.  Soc.,  107,  76  (1915);  Brauner  and  Krepelka,  /.  Am.  Chem. 
Sec.,  42,  924  (1920). 

1  Baxter  and  Starkweather.  Proc.  Nat.  Acad.  Sci.,  107,  76  (1915);  /.  Am.  Chem. 
Soc.,  42,  905  (1920). 


26 


was  not  clear,  distinct  dark  patches  being  present.  This  had  been  asso- 
ciated by  experience  with  an  overweight  of  precipitate,  so  the  data  are 
chiefly  of  value  in  showing  the  readiness  with  which  slight  impurity  in 
the  silver  bromide  can  be  recognized  by  obvious  defects  in  the  fused  mass. 

With  further  experience  thus  accumulated,  with  every  confidence  in 
the  purity  of  the  silver  and  the  bromine,  and  with  renewed  assurance  as 
to  the  accuracy  of  the  volumetric  determination,  attention  was  turned 
to  the  analysis  of  the  three  carefully  prepared  series  of  antimony  bromide 
samples. 

The  manipulation  involved  in  the  final  analyses  was  not  altered  in  any 
essential  detail  from  that  already  described  in  connection  with  the  pre- 
liminary series.  The  greater  uniformity  of  results  is  due,  undoubtedly, 
to  increased  skill  in  manipulation  acquired  during  the  earlier  work.  The 
slightly  higher  value  may  well  be  due  to  purer  materials  being  combined 
in  the  preparation  of  these  final  series. 

Final  Analyses. — Series  B  and  D  were  prepared  from  antimony  ob- 
tained by  reducing  the  oxide  in  hydrogen.  Series  C  was  prepared  from 
antimony  obtained  by  fusing  the  oxide  with  sodium  cyanide. 

TABLE  OP  FINAL  ANALYSES. 
Summary  of  Series  B  (by  hydrogen). 


Sample 
No.       Weight. 

Wt.  Ag. 

Ratio  I       At.  wt.  Sb 
SbBrs:3Ag.    from  R  I. 

Wt.            Ratio  II 
AgBr.      SbBf3:3AgBr. 

At.  wt.  Sb 
from  R  II. 

Ratio 
Ag:AgBr. 

I 

4 

.  17410 

3.73672 

1.11705 

121.771 

6. 

.50517 

0.641659 

121 

.754 

0.57442 

III 

4 

.97693 

4.45524 

1.11710 

121.787 

7. 

75589 

0.641697 

121 

.775 

0.57443 

IV 

5 

.97344 

5.34702 

1.11715 

121.803 

9. 

30873 

0.641703 

121 

.779 

0.57441 

V 

5 

65589     5.06310 
Average 

1.11708 

121.781 

8. 

81443 

0.641663 

121 

.756 

0.57441 

1.117095 

121.786 

0.641680 

121 

.766 

0.574418 

Summary 

of  Series 

C 

(by  cyanide). 

I 

3 

.64686 

3.26462 

1.11709 

121.784 

5 

.68301 

0.641713 

121 

.784 

0.57445 

III 

3 

.64435 

3.26258 

1.11701 

121.758 

5 

.67970 

0.641645 

121 

.746 

0.57443 

IV 

3 

.35749 

3.00574 

1.11703 

121.765 

5 

.23284° 

0.641619° 

(121 

.731) 

0.57440° 

V 

2 

.92082 

2.61469 
Average, 

1.11712 

121.794 

4 

.55149 

0.641728 

121 

.793 

0.57445 

1.117063 

121.777 

0.641679 

121 

.764 

0.574433 

Summary  of  Series  D  (by  hydrogen). 

I 

3 

.390,50 

3.03541 

1.11699 

121.752 

5 

.28506° 

0.641525° 

(121 

.678) 

0.57434° 

II 

4 

.32024 

3.86739 

1.11709 

121.784 

6 

.73334° 

0.641619° 

(121 

.731) 

0.57436° 

III 

4 

.70518 

4.21221 

1.11703 

121.765 

7. 

.33279 

0.641663 

121 

.756 

0.57443 

Average   1.117037  121.767 
°  Silver  bromide  showed  dark  specks  when  fused. 
Average  of  11  vol.  del.  =  121.777. 
Average  of  11  grav.  det.  =  121.753. 
Average  of  8  grav.  det.  =  121.768. 
Average  of  11  vol.  det.  and  11  grav.  det.  =  121.765. 
Average  of  11  vol.  det.  and  8  grav.  det.  =  121.773. 


0.641602     121.722    0.574377 


27 

Series  B  was  from  Preparation  I  of  antimony  (reduced  in  quartz).  A 
total  of  7  bulbs  was  collected,  the  first  and  last  being  discarded.  The 
numbers  in  the  series  represent  the  bulbs  in  the  order  in  which  they  were 
filled.  No.  2  was  spoiled  in  the  analysis. 

Series  D  was  from  Preparation  II  of  antimony  (reduced  on  a  lime  sup- 
port). A  total  of  9  bulbs  was  collected.  No  first  sample  was  discarded. 
The  numbers  in  the  series  represent  the  bulbs  in  the  order  in  which  they 
were  filled.  No.  2  was  lost  in  the  analysis. 

Series  C  was  from  Preparation  III  of  antimony.  A  total  of  10  bulbs 
was  filled,  Nos.  5  and  6  being  lost  in  sealing  up.  No  first  sample  was  dis- 
carded. The  numbers  in  the  series  represent  the  bulbs  in  the  order  in 
which  they  were  filled. 

It  is  noted  that  the  volumetric  result  on  each  sample  is  checked  more 
closely  by  the  corresponding  gravimetric  result,  when  the  fused  silver 
bromide  was  clear,  than  by  the  other  volumetric  results  within  the  series. 
Therefore,  it  seems  proper  to  refer  the  small  variations  among  the  differ- 
ent samples,  less  to  the  analytical  process  following  the  filtering  of  the  solu- 
tions, than  to  slight  deviations  in  accuracy  of  weighing,  in  accuracy  of 
applying  vacuum  corrections  and  in  accuracy  of  the  whole  manipulation 
from  the  breaking  of  the  bulb  to  the  washing  of  the  glass. 

It  is  customary  to  attempt  to  reduce  the  magnitude  of  individual  errors 
to  one  part  in  100,000.  Assuming  that  the  volumetric  determinations 
are  slightly  more  accurate  than  the  gravimetric  determinations,  it  is  to 
be  observed  that  the  maximum  variation  among  the  ratios  calculated 
for  SbBr3  :  3Ag  is  from  1.11715  (maximum)  to  1.11699  (minimum),  a 
variation  of  14.3  parts  in  100,000.  With  the  complexity  of  manipula- 
tion involved  in  the  analytical  procedure,  this  may  be  regarded  as  repre- 
senting a  concordance  comparing  favorably  with  other  atomic  weight 
work  of  the  present  day. 

The  mean  of  Series  B  varies  from  that  of  Series  D  by  5.2  parts  in  100,- 
000,  while  the  average  of  Series  B  and  D  varies  from  the  mean  of  Series 
C  by  only  0.27  part  in  100,000. 

In  calculating  atomc  weights  from  analytical  data  of  the  halide  to  silver 
or  silver  halide  type,  it  is  to  be  noted  that  variation  in  the  ratio  is  multi- 
plied by  the  valence  of  the  metal.  The  11  volumetric  determinations 
average  121.777  with  a  so-called  "probable  error"  of  0.003,  while  the  8 
acceptable  gravimetric  determinations  average  121.768  with  a  "probable 
error"  of  0.004. 

The  average  from  11  volumetric  and  8  gravimetric  determinations  is 
121.773,  the  most  probable  atomic  weight  of  antimony. 
Note  on  Cooke's  Bromide. 

Since  the  number  assigned  as  the  atomic  weight  of  antimony  has  for 
many  years  been  based  on  the  work  of  Cooke  in  which  a  material,  given 


28 

the  formula  SbBr3,  was  analyzed  for  bromine;  it  is  peculiarly  of  interest 
that  in  the  work  here  reported  a  material  of  the  same  assigned  formula 
has  been  studied.  Careful  examination  of  Cooke's  paper  makes  it  evi- 
dent that  the  difference  must  be  assigned  chiefly  to  the  compositions  of 
the  materials  studied  rather  than  to  later  refinements  of  the  analytical 
process.  Cooke's  method  of  preparation  included  repeated  distillation 
from  metallic  antimony,  several  recrystallizations  from  carbon  disulfide, 
and  repeated  fractional  distillation.  In  the  last  work  this  product  was 
twice  sublimed  in  a  current  of  carbon  dioxide.  In  the  earlier  work  the 
recrystallized  material  was  analyzed.  The  average  results  were  the  same, 
though  the  variations  were  large  in  the  earlier  work.  The  description  of 
the  whole  process,  however,  shows  that  all  handling  of  material  involved 
exposure  to  air  and  that,  in  the  earlier  part  of  the  preparation,  there  was 
considerable  opportunity  for  the  absorption  of  moisture.  Furthermore, 
while  the  carbon  dioxide  used  in  the  process  of  sublimation  is  described 
as  "absolutely  dry,"  careful  search  fails  to  reveal  the  use  of  drying  agents 
other  than  sulfuric  acid  followed  by  calcium  chloride.  Nor  is  any  state- 
ment made  as  to  method  of  drying,  distilling  flasks,  receivers,  etc.  Aside, 
therefore,  from  carbon  disulfide,  used  in  the  recrystallization,  the  chief 
difference  between  the  preparation  by  Cooke  and  that  just  described  would 
appear  to  lie  in  the  relative  exposure  to  moisture. 

In  the  work  just  completed,  probably  greater  care  has  been  taken  in 
the  drying  of  the  initial  materials  and  apparatus  than  has  been  described 
in  the  recent  work  on  the  halides  of  phosphorus  and  of  tin  where  the  re- 
sults of  analyses  have  been  regarded  as  entirely  trustworthy. 

It  may  be  worth  while  to  suggest  a  way  in  which  moisture  might  ac- 
count for  the  difference  obtained.  Assuming  the  reaction 

SbBr3  +  H2O  =  SbOBr  +  2HBr, 

and  knowing  the  readiness  with  which  complex  bromides  are  formed,  it  is 
possible  that  the  process  of  crystallization  and  distillation  may  leave  a 
product  containing  a  small  amount  of  hydrobromic  acid.  During  the  sub- 
limation this  may  again  condense  with  the  crystals  in  the  receiver;  or  from 
incomplete  drying  of  the  carbon  dioxide,  a  trace  of  moisture  interacting 
with  the  molten  antimony  bromide  may  supply  extra  hydrogen  bromide 
such  that  the  amount  retained  by  the  sublimate  is  the  same  as  that  in 
the  original  material. 

Direct  comparison  of  the  bromine  content  to  correspond  to  the  two 
values  for  the  atomic  weight  gives  the  following: 

Atomic  weight.  %  bromine. 

120.0  66.643 

121.77  66.317 


Difference,    0 . 328 


29 

If  this  difference  is  assumed  to  be  due  to  the  cause  suggested  the  material 
studied  by  Cooke  had  the  approximate  composition,  99%  SbBr3,  1%  HBr 

Summary. 

In  an  all-glass  apparatus,  3  preparations  of  antimony  were  combined 
with  bromine,  the  resulting  product  twice  distilled  under  a  pressure  of 
5  to  10  mm.  while  gaseous  materials  could  yet  be  removed,  then  distilled 
a  third  time  under  less  than  one  mm.  pressure  into  a  series  of  small  bulbs 
which  were  sealed  off  from  each  other  as  individual  samples.  From  the 
time  the  pure  dry  materials  were  placed  in  the  apparatus  till  the  bulbs 
were  broken  under  tartaric  acid  solution,  only  inert  gases  came  into  con- 
tact with  the  preparation.  The  resulting  product  was  analyzed  for  bro- 
mine in  two  ways;  first,  by  finding  the  amount  of  silver  equivalent  to  the 
sample  in  the  usual  way;  second,  by  adding  excess  of  silver  nitrate,  then 
filtering  out  and  weighing  the  silver  bromide.  Precautions  taken  and  cor- 
rections applied  include  all  described  within  recent  years  in  similar  work. 
In  eleven  analyses  a  total  of  46.76580  g.  of  antimony  bromide  required 
41.86463  g.  of  silver  and  formed  72.88245  g.  of  silver  bromide.  The 
ratios  are  1.117074  and  0.641611,  from  which  the  respective  values  for 
the  atomic  weight  of  antimony  would  be  121.799  and  121.755.  If  for 
the  antimony  bromide  to  silver  bromide  ratio  samples  C-IV,  D-I  and  D-II 
are  omitted  since  in  these  cases  the  fused  silver  bromide  did  not  give  a 
clear  mass,  the  weights  would  be  35.69757  g.  of  antimony  bromide  to 
55.63121  g,  of  silver  bromide,  corresponding  to  an  atomic  weight  of 
121 . 767.  The  ratios  of  silver  to  silver  bromide  are  0 . 574413  and  0 . 574427, 
according  to  whether  the  imperfect  silver  bromide  determinations  are 
included  or  omitted.  Baxter's  determinations  of  this  ratio  gave  0.57445. 
Averaging  the  volumetric  results  for  the  11  samples  with  the  gravimetric 
results  for  8  samples,  the  most  probable  atomic  weight  for  antimony  (as- 
suming Ag  =  107.880)  becomes  121.773. 


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